Photoelectric timer for x-ray apparatus



Feb. 13, 1951 J. BALL ET AL PHOTOELECTRIC TIMER FOR X-RAY APPARATUSFiled Nov. 13, 1947 TO X- RAY TRANSFOR MER (K 88- 5 880. s s

91b 92b INVENTORS JACK BALL & EDWARD B GRAVES 736% a flm AT TOR NEYSPatented Feb. 13, 1951 PHOTOELECTRIC TIMER FOR X-RAY APPARATUS JackBall, Cleveland, and Edward B. Graves,

South Euclid, Ohio, as

signorsto Picker X-Ray Corporation Waite Manufacturing Division, Inc.,Cleveland, Ohio, a corporation of Ohio Application November 13, 1947,Serial No. 785,664

9 Claims.

This invention relates to improvements in a photoelectric timer for usein connection with X-ray apparatus for Roentgen photography.

The purpose and theory of the type of apparatus here disclosed is fullyset forth in United States Patent No. 2,401,289, granted May 28, 1946,to Russell H. Morgan and Paul C. Hodges, to which reference may be hadfor an explanation of the theory. The present invention provides animprovement over the above mentioned 1 patent.

In the Morgan, Hodges patent and in the present application use is madeof a phototube of the general type disclosed in United States LettersPatent No. 2,231,697, granted February .11, 1941,

to Vladimer K. Zworykin et al. In such a phototube there is provided alight sensitive cathode, an anode, and a series of multiplyingelectrodes called dynodes. Visible radiation produced on a fluorescentscreen by an X-ray exposure fell upon the light sensitive cathode and,through the multiplying electrodes, resulted in an output which wasutilized to charge a condenser. When a sufiicient charge accumulated onthe condenser,

it tripped a trigger tube for terminating the X- ray exposure Morgan andHodges used a Thyratron type control tube. Since this tube is anegative-control tube, they found it necessary, as set forth in theabove mentioned Patent No. 2,401,289, to use the ninth 'dynode as acollector so as to obtain a charge of the right polarity to trip thetrigger tube since the plate or anode of the phototube would give anegative charge as it is the receiver of electrons. This patented devicecut down the sensitivity obtained. It is an object of the presentinvention to use the plate of the phototube for the tripping of thetrigger tube so as to obtain greater sensitivity. 7

In an attempt to get better results Morgan and Hodges tried differenttypes of trigger tubes and also tried an amplifier between the phototubeand the trigger tube. Difficulties were still encountered because anegative potential was supplied on the control grid or starter anode ofthe trigger tube and at the same time, a positive voltage was beingapplied to the plate of the trigger tube. They were therefore workingthis tube in what is termed the second quadrant which is frowned upon bytube manufacturers, who state that the tube operation in anything butthe first quadrant will cause the operation to be very erratic andunstable. Operation in the first quadrant calls for a positive potentialon the control grid and apositive potential on the plate of the triggertube. It is an object of the present invention to so connect the triggertube that itis operated in the first quadrant.

Another object of the present invention is the control of thesensitivity of the phototube in a novel manner. Standard methods knownto us,

use a series resistor from the high voltage power supply so asto raiseor lower the total voltage across the phototube. Another dimculty withthis type of control is that if the total voltage is reduced too muchthe output of the tube drops excessively with resultant erratic responsefrom the phototube. It is an object of the present invention, therefor,to maintain the total voltage fixed and to vary the voltage of one ofthe dynodes of the phototube in'a potentiometer type circuit. In this:manner we obtain a control which has a much greater range 'ofsensitivity than the series type mentioned above.

A further object of the present invention is to incorporate certainsafety devices so that upon failure of current or failure of importantportions of the apparatus, the X ray tube will be protected.

Still afurther object of the invention is the incorporation of aninterval timer in combination with the photoelectric timer so that ifthe latter fails to terminate the X-ray exposure within a safe timelimit, the interval timer will take over.

Other objects and advantages of our invention will be apparent from theaccompanying drawings and description and the essential features thereofwill be set forth in the appended claims.

The drawing is a diagram showing one manner of applying our invention.

A source of alternating current at the usual potential of about '115volts is indicated at Ll L2. Connected between these lines is line [0including a push button I l which is used to cause an X-ray exposure. Inseries in this line is a relay [2 having three armatures in, 422) andl2e which are indicated in dot-dash lines adjacent the relay but arerepeated in full lines in the proper place in the diagram. This is doneto simplify the diagram. Also connected across the source Ll, L2" bymeans of line 8 is the primary [3a of a power transformer 53. Thistransformer has several secondaries as indicated at 13?), I30, l3d, 36and 13]. A peaking transformer It has a primary lid connected by line Itto the source Li, L2. In series in this line is a resistor It andthe'armature l2?) of the relay l 2 mentioned above. The secondary lib oftransformer It is connected to the control grid llc of an exposureinitiating tube ii of the Th'yratrontype through a resistor it. Thefilament Me of this tube is supplied from the secondary it?) of thetransformer I3. The plate lla is connected in a circuit which includesline 19, armature of relay l2, relay 28, line 2!, resistor 22, line 23and the cathode l'ld. It results from this circuit that upon closing thepush button H, the relay I2 is immediately energized and this closes theplate circuit of tube ll through the armature I20. However no currentflows because of a negative bias on the tube I? as will presently bedescribed. At the first positive voltage peak through the transformerI4, the control grid I'Ic becomes positive and the tube I7 passescurrent through the plate circuit described so that relay 2c isenergized. This relay has an armature 25a shown near the bottom'of thediagram and through a circuit to be more fully described later andimmediately energizes a relay 2c which closes the contacts 25 whichcompletes a circuit to the X-ray transformer so as to initiateanexposure. .The tube I'I, having a direct current energizing sourceremains locked in until the armature I2c opens. It is thus possible toutilize the positive impulse through the peaking transformer I4 and thetime delay until contacts 25 close, to close the circuit to the X raytransformer at a point of zero potential.

A source of rectified current is provided for tube I? and for certainother purposes as will presently appear by means of the secondary I30 ofthe transformer I3. A rectifier tube 26 is provided having a pair ofplates 26a connected to opposite ends of the secondary winding I30 whichhas a central tap for the line 21 which of course will be the negativeside of the rectified circuit. The filament 26b of the tube is suppliedfrom the secondary. I311 of transformer I3. This filament isconnected'to line 28 which is the positive side of the rectifiedcircuit. The rectified current is filtered by. resistor 22 and condenser29. This rectified current is supplied to the plate Ila of tube I'Ipreviously mentioned. The negative side of the circuit, line 27, isconnected through line 39, transformer winding lb and resistor I8 to thecontrol grid Ilc giving the same a negative bias until overcome bypositive peaks from transformer I4 as previously described. The screen-grid ilb isconnected by line 23 to a tap 22a which is more positivethan the point 22b.

A trigger tube 3! is shown as of the cold cathode 'type although it willbe understood that a hot cathode or filament type tube might besubstituted. The plate 31a. of this tube is connected to line 28 throughrelays 32 and 33 in parallel. These relays have arinatures 32a and 33afor purposes Which will later appear. The cathode '3 lb is connected toline 21'. The grid 3Ic is connected through resistor 34 to ground for apurpose which will later appear.

A phototube of the above-mentioned Zworykin type is diagrammaticallyshown at 3 3. This tube .has a plate 3 3a, a cathode 34b and a pluralityof dynodes 340 which are numbered from one to nine. It should beunderstood that this showing is purely diagrammatic and that dynodes inthe .Zworykin tube are actually staggered to produce a particularmultiplying effect. The current supply for the phototube is providedthrough transformer 35 which has a primary 35a connected between linesLI and L2 .by conductors 35 and 3?. Avoltage regulator tube 38 isprovided having a plate 38a connected to one end of the winding 35a anda cathode 38%) connected to the other end of the samewinding. Thisstabilizes the voltage supplied at transformer 35. A variable resistor39 is provided in line 37. The output of the sec- 'ondary 35b oftransformer 35 is rectified through tub 40 which has a plate 40aconnected to one end of the winding 35b and a filament 4% which issupplied through lines AI and 62 from the secondary l3? of transformerI3. The negative side of this rectified circuit is connected throughline 4 end of resistor 4d. The positive side of therec tified circuit isconnected through line 45, variable resistor 56, fixed resistor 41 andresistors 48 and 39 in parallel, with the negative end of resistor W.This rectified current is filtered through condenser 50 and resistor 5|.Suitable taps on resistor 44 supply dynodes one to eight inclusive ofthe phototube. The ninth dynode is connected to switch 52 which in thefull line position shown in the drawings engages contact 52a forradiography. This contact is connected through line 53 with a tap on theadjustable resistor 48. Switch 52 may also be moved to the dot-dashposition to contact 522) for photofiuorography The contact 5% isconnected by line 54 with a tap on the adjustable resistor s9. By makingthe voltage on number 9 dynode equal to that on number 8 dynode there isprovided a minimum sensitivity of the photo'- tube. Making the number 9dynode approximately 100 volts higher than the number 8 dynode gives amaximum sensitivity. The series resistor 46 is used as a calibrator. Thephototube units are sent out fully assembled including the parts withinthe broken line 55. By adjusting the resistor (it, each phototube unitmay be adjusted to the same sensitivity so as to give identical output.

A capacitor 56 is pro-vided for collecting the electrons from the anode34a of the phototube until a sufiicient charge is collected to fire thetrigger tube 3 I. This condenser is connected with line 51 which in turnconnects the anode 34a of the phototube with the cathode 3Ib of thetrigger tube. The other 'side of the condenser is grounded through line58. The capacitor 56 is normally short-circuited through line 59 andswitch 200 until an exposure starts. At that time, the switch 200 opensand the capacitor begins to collect a charge. capacity of the capacitor56, the potential to which it is charged in order to fire the triggertube and the sensitivity of the phototube, an exposure may be terminatedwhen a recording film has been properly exposed.

As previously stated, we work the trigger tube in the first quadrant'inthe following manner. The grid 3Ic of the trigger tube is maintained atground potential. The potential of the cathode 3Ib is then raised in anegative direction as it receives charges from electrons collected attheanode 34a of the phototube. Making the cathode 3Ib negative with respectto the grid 3 I0 is electrically the same as making the grid positivewith respect to the cathode and since wehave the plate 3Ia. at apositive voltage, we are'working the trigger tube in the first quadrant.Thus, we are able to get stability and longlife without the use of anyamplifier tube such as has been attemped by others as previouslyexplained.

The capacitor 56 as described above in one form of our device has acapacity of .01 microfarad for use in radiography carried out in thefashion disclosed in United States Patent No; 2,401,289 mentionedpreviously. We may also equip our device with another capacitor 60which, by means of lines SI and 62 and switch 63 may be connected inparallel with the capacitor 56 by throwing the switch 63 to the dot-dashposicopending application at Edwin R. Goldfield.

By proper selection of the drawing.

"passes through line l6 and relay Tl. terminate the X-ray exposure if ithas not prenob'ert J. stava and Edgar-J. Bastin, Jr.,=seria1 N0. 24172,filed ct0'ber 24, 1945, now Patent 23961089. Sensitivity" adjustment forradiography and photofiuorography is maintained by means of thepotentiometers 48 and 49'respectively. The dot-dash 'line connectingswitches 52 and 63 indicates that these switches are ganged to move'taneously in one position and engage 52b and 53b simultaneouslyinth'e-o'ther position. -Me'an's ispiovided for terminating an exposureafter a predetermined interval in case the photo timer should fail. Thismeans includes a'trigger tube '64 of the Thyratron type having-an anode64a, a screen grid 64b, a control grid 64C and a cathode 64d. Thefilament s le'is energized through lines E and'se which are connectedwith the secondary I 3 of the power transformer l3. A condenser e1normally floats across the line Ll, L2 in charged-condition.Thischarging circuit comprises line 68, resistor 69, cathode 64d, grid64c,

resistor l a, line .1 l variable resistor 12, line 66,

transformer winding l3f, 1ine65 and 1ines13 and M. The switch 2% betweenlines 68 and "is normally in open position as indicated in the At thestart of an exposure, switch '2b is moved'tobonnectlines-Gfi and 14.This stops the charge of condenser 61 while connecting the cathode 84dto L2 and the plate 64a to Ll. The condenser 6'1then discharges'slowlythrough a resistance bank i'n'dicated at 15. A rough time adjustmentmaybeobtained in that portion of thebaiik indicated at 'iEa'while afiner adjustment may be provided at b. Thenegative'plate of thecondenser 67 is-connected to the control "grid 64c and no current willpass tube 64 until the charge has leaked off condenser 6'! to thethreshold of tube 64. When control grid 64c passes this pointthe tube 64fires and current This will for the purpose of correctingthe intervaltimer for variations in line voltage.

The winding I3 is so connected'in thecircuit for chargingcondensert'l'that its voltage bucks the charge voltage and therefore-anincrease in the linevoltage will automatically decrease the charge oncondenser Bl which' willdecrease the time interval necessary to firetube 64.

For the purpose of indicating the general control of theX-ray exposure anumber of switches have been assembled in the wiring diagram at one endthereof so as to illustratethe various ways in which the'exposure maybemade or broken. This series of connections beginning at Ll comprises therelay winding 2:2 which controls the contacts 25 which energize theX-ray transformer during an exposure. Next comes the switch 2a which isenergized by the relay' previously described. The switch 86a is'normallyopen but is -closed-immediately'upon the energization of the winding H3ofthe power transformer i3. Upon 'i'ailure of this power supply, relay80 would be deenergized and swit'chfill would open. Line iii connectsswitch Sllwto switch 'llo which is'nor- "m lll los d ea nstthecontacttzasshowndn "him to record "X-rays'which havepassed throughphotofluorography itengages contact oil).

brokenline-Eii indicates that this swtich insiee:

tube assembly.

the drawing when relay' 'ilis deenergized. If the intervaltimeroperatessoas to energize relay ll in the manner described above, the switch Tiaengages contact 83 which will light a lamp '34 'or other'signal-toindicate that the interval timer has terminated the exposure rather thanthe photo timer. At the same time that switch 11a engages contact-B33it-completes a circuit through lines 85, 86 and (it toenergize relay ccwhich is in line 85. This'relay has an armature 88c which is normallyopen as shown in the drawing but which closes upon energization of relay'88 so-as to lock the-relay in'through lines and The signal 22%therefore remains energized so that the operator will make the necessarycorrections to "return to'the control of the photo timer.

The'line connects switch @162 to switch 32a which is normally closedbutisopene'd by energization of relay 3T2 whentrigger tube 3| fires uponoperatiorr'of the photo timer to terminate the X-ray exposure. 'I'heline t'l leads to aswitch fill which ganged with switches 52 and asindicated by the dot dash lineconnecting them. For radiography theswitch engages contact his and for thephoto timer assembly. Outside ofthis assembly is-ani'anual switch'ii? having positions silo and 92bcorresponding respectively to the:

'toenergize the peaking transformer 54. It also closes switch [2c inline it so as to place the relay 2!? in circuit with tube ll. Uponoccurrence of the first positive peak in transformer winding use, tubefl passes current and energizes relay This closes switch 2501 whichenergizes relay at to close the X-ray transformer contacts 25 apredetermined'tinie after the potential peak from transformer i i and,as previously mentioned, this is so adjusted as to close the X-raytransformercontacts at zero potential. As previously mentioned, theswitch this is closed when power transformer is is energized providingthe winding [3 is in proper condition. Relay 20 also closes'switch 2%connecting lines it and 58 so as to cause the interval timer to beginits operation as previously described. Relay 2 also opens switch 200 inline 55. so that capacitor 55 (or 55 plus E50) begins to collect acharge for the opera tion of thephoto timer as previously described.

If'thephoto timer terminates the exposure by firing of the tube 3!,relays 33 and 32 are energized. Relay 33 when energized will open switch330: in line 76 of the interval timer circuit so as to reset that timerfor the next operation. Relay 3 2 will open switch 32a to deenergizerelay 24, permitting contacts to open and terminate the X-ray exposure.Upon the release of button it relay i2 is deenergized and the'circuitswitches 12a, 12b and I20 are returned to their original positions so asto set the parts for another operation.

1.In apparatus-fortimingthe exposure of a a body and are incident upon afluorescent screen,

7 whereby electrons from said phototube anode may charge said triggertube cathode negatively to cause said trigger tube to fire.

2. In apparatus for timing the exposure of a film to record X-rays whichhave passed through a body and are incident upon a fluorescent screen,thecombination of a phototube having an anode and a light sensitivecathode and multiplying electrodes, a trigger tube having an anode and acathode and a control grid, switch means operatively connected with anelectrical circuit sensitive to firing of said trigger tube forterminating said X-ray exposure, an electrical circuit normally biasingsaid trigger tube beyond cutoff, a capacitor in circuit with saidphototube and said trigger tube, and an electrical connection from saidanode of said phototube to said cathode of said trigger tube, wherebyelectrons from said phototube anode may charge said capacitor to apotential sufiicient to charge said trigger tube cathode negatively tocause said trigger tube to fire.

3. In apparatus for timing the exposure of a film to record X-rays whichhave passed through a body and are incident upon a fluorescent screen,the combination of a phototube having an anode :and a light sensitivecathode and multiplying lelectrodes, atrigger tube having an anode and:a cathode and a control grid, switch means opieratively connected withan electrical circuit sensitive to firing of said trigger tube forterminating said X-ray exposure, an electrical circult applying apositive potential in the plate circuit of said trigger tube, anelectrical circuit normally maintaining said control grid at arelatively fixed potential below the threshold of said trigger tube, anda capacitor in circuit with said phototube anode and said trigger tubecathode andso arranged that electrons collecting on said phototube anodemay charge said capacitor to a potential sufiicient to charge saidtrigger tube cathode negatively and to cause said trigger tube to fire.

4. In apparatus for timing the exposure of a film to record X-rays whichhave passed through a body and are incident upon a fluorescent screen,the combination of a phototube having an anode and a light sensitivecathode and multiplying electrodes, a trigger tube having an anode and acathode and a control grid, switch means operatively connected with anelectrical circuit sensitive to firing of said trigger tube forterminating said X-ray exposure, an electrical circuit applying apositive potential in the plate circuit of said trigger tube, anelectrical connection from said control grid to ground, an electricalconnection from taps connected consecutively to the other multiplyingelectrodes of said phototube to render them consecutivelymore positive,whereby said electrode nearest said anode is used to vary thesensitivity of said phototube.

6. In a phototube for timing the exposure of a film to record X-rayswhich have passed through a body, said phototube being of the typehaving an anode and a light sensitive cathode and multiplyingelectrodes, the provision of a resistor having spaced taps connectedconsecutively to all but one of said multiplying electrodes to renderthem consecutively more positive, and separate means for varying thepotential of said one of said multiplying electrodes to vary thesensitivity of said phototube.

7. In a phototubefor timing the exposure of a film to record X-rayswhich have passed through a body, said phototube being of the typehaving an anode and a light sensitive cathode and multiplyingelectrodes, the provision of a resistor having spaced taps connectedconsecutively to all of said multiplying electrodes except that one ofsaid electrodes in circuit nearest said anode of said photo tube torender said electrodes consecutively more positive, and separate meansfor varying the potential of that one of said multiplying electrodes incircuit nearest said anode of said phototube, whereby to vary thesensitivity of said phototube.

8. The combination of claim 3 including an interval timer having asecond trigger tube. means biasing a control grid of said second triggertube beyond its firing threshold and including a second capacitor incharged condition, means normally charging said second capacitor to apredetermined potential, resistor means in circuit with said secondcapacitor to provide a controlled leaking oil of its charge to a pointwhere said second trigger tube will fire, means responsive to firing ofsaid second trigger tube for terminating said X-ray exposure, switchmeans normally short-circuiting said first named capacitor, and meansoperable by initiation of an X-ray exposure for opening saidshort-circuiting means of said first named capacitor and forsynchronously interrupting said second capacitor charging means, wherebytwo alternative timing. circuits are available for terminating saidX-ray 'exposure.

9. The combination of claim 1 including two separate fixed resistorsadapted to be placed alternatively in circuit with one only of saidmultiplying electrodes for varying the potential of said one of saidmultiplying electrodes, and switch means for connecting a selected oneof said fixed resistors in said last named circuit whereby to providetwo alternatively selected fixed sensitivities for said phototube.

JACK BALL.

EDWARD B. GRAVES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,159,755 Zworykin et al May 23,1939 2,244,137 Bischoff et al. June 3, 1941 2,252,752 Bliss Aug. 19,1941 2 ,401,289 Morgan et a1 May 28, 1946 2,417,023 Sweet Mar. 4, 19472,441,324 Morgan et al May 11, 1948 2,454,168 Hartwig Nov. 16, 19482,459,632 Engstrom Jan. 18, 1949

